1. Technical Field
This invention relates to the dyeing of cationic nylon with fiber reactive vinyl sulfone type dyes.
2. Background of the Invention
For years attempts have been made to produce a printed nylon yarn by space dyeing and other techniques which could be tufted into carpet and maintain its color integrity during subsequent dyeing operations. Space dyeing, i.e. the dyeing or printing of a knitted fabric is well known in the art. Such attempts have been generally unsuccessful due to two problems. First, the acid dyes which they use to print the yarn migrate off the substrate into the dyebath at the boiling temperatures and redeposit on the greige yarn. For example, if a dark blue shade was space dyed onto a yarn that was then tufted into greige carpet and finally overdyed a pale yellow shade, some of the blue acid dye will cross stain the yellow base shade and produce a greenish shade. The second problem was that the monosulfonated acid dyes normally used to dye solid carpet shades will also cross dye the space dyed area. An example of this would be a pale blue shade on the space dyed yarn which was implanted in a carpet that was overdyed a dark red shade. The red acid dye, chosen for its migration power, will also dye unoccupied dye sites in the blue printed areas and shift the blue to a purple shade.
Attempts to overcome these problems have included the use of premetalized acid dyes, fixing agents, low temperature and low pH dyeing cycles, light acid dyeable nylon, Suessen heat setting, etc. The most commonly used system consists of a combination of the premetalized acid dyes and sulfonated phenol formaldehyde condensates, which are the typical acid dye fixing agents. The premetalized dyes are large molecules which are not very mobile and do not tend to migrate from the printed area onto the greige carpet during overdyeing. The phenol formaldehyde fixing agents form a shield or film around the fiber which prevents the print or space dyed colorant from migrating and also inhibits the cross dyeing of the base shade into the printed area. This approach has been somewhat successful in continuous overdyeing applications, but it fails in exhaust dyeing applications where the substrate is held at the boil for 30-60 minutes. An additional problem with premetalized acid dyes is that they are limited in their range of shades and are usually dull in cast, which prevents the achievement of bright yellows, reds, blues, and greens.
There have also been systems where the exhaust overdyeing was carded out at low temperatures (160.degree.-180.degree. F.) and low pH (4.0-5.0)in order to limit the migration from the printed area. The problem with this approach was that the overdye shade was often unlevel, and attempts to repair it by raising the pH or temperature caused the print dyes to migrate off the fabric into the substrate dyebath. Other approaches include the use of the premetalized dyes and fixing agents with light dyeable nylon and Suessen heat setting. The cross staining of the overdye shade is reduced because the light dye nylon has fewer dye sites and Suessen heat setting destroys dye sites, but this process gives unacceptable results in exhaust overdye situations.
Several years ago, a system was perfected where vinyl sulfone dyes could be used to space dye nylon so that total overdye fastness was achieved. The vinyl sulfone dye was first pretreated with alkali to convert the ester into the vinyl group, and then it was printed and steamed on the acid side forming an ionic bond with the amine end groups of the nylon. After washing the printed nylon was dipped into alkali, dried, and heat set. When the vinyl sulfone dyes undergo heat setting under alkaline conditions, they will form a reactive or covalent bond with the amine groups. Since the vinyl sulfone dyes formed a reactive bond with the nylon, they will not migrate from the space dyed areas even under the most severe dyeing conditions such as exhaust dyeing under pressure. Therefore, this process solved half of the space dye/overdye problems, but difficulties with cross dyeing were still encountered. When regular dye nylon was printed with the vinyl sulfone dyes, all of the available dye sites could never be quite fully occupied, so if a blue shade was overdyed on carpet containing the space dyed yarn, the print shades would always be shifted to the blueside and appear duller in cast. Fixing agents cannot be used with the vinyl sulfone dyes so it was not possible to form a film barrier around the printed areas which would resist the cross staining to a degree.
To overcome the cross staining or cross dyeing of the space dyed area, the use of cationic dyeable nylon was investigated. Cationic dyeable nylon is made by incorporating SO.sub.3 groups into the polymer (U.S. Pat. No. 3,542,743) in a number sufficient to render the nylon dyeable with basic dyes. However, there are still a certain number of amine end groups left in the cationic dyeable nylon that remain receptive to acid type dyes and cross staining is a problem.